Most modern wind turbines are controlled and regulated continuously most often with the purpose of ensuring maximum power extraction from the wind under the current wind, and weather, while at the same time ensuring that the loads on the different components of the wind turbine are at any time kept within acceptable limits. Desirably, the wind turbine may also be controlled to account for fast sudden changes in the wind velocity—the so-called wind gusts, and take into account the dynamic changes in the loads on the individual blades due to e.g. the passing of the tower, or the actual wind velocity varying with the distance to the ground (the wind profile or shear).
To this purpose a number of parameters are collected and monitored by the controllers in a wind turbine, such as for instance the current wind speed and direction, the rotational speed of the rotor, the pitch angle of each blade, the yaw angle, information on the grid system, and measured parameters (e.g. stresses or vibrations) from sensors placed e.g. on the blades, the nacelle, or on the tower.
Based on these and following some control strategy the optimal control parameters of the turbine in order to perform optimally under the given conditions are determined. The current performance, and thereby the power production and the load situation of the wind turbine is primarily controlled by controlling the pitch angles of the blades, but may further include adjusting for instance any different active aerodynamic devices for changing the aerodynamic surfaces of the blades such as flaps or vortex generating means, adjusting the power, and/or adjusting the rotational speed of the rotor.
Wind turbines are traditionally constructed and controlled according to standards and according to wind maps and incorporating the trade-off of maximizing the annual energy production by the wind turbine while on the same time ensuring a certain life time of the turbine i.e. keeping the loads on the different components of the wind turbine within acceptable limits at all times and over time. Wind turbines are therefore typically designed according to a certain (high) turbulence but will most often be operating at a lower turbulence level and may in some conditions be controlled too conservative, while in some conditions not conservative enough resulting in undesired fatigue or extreme loads on the wind turbine components, especially the blades, nacelle and tower.
Traditional wind turbines are designed for a specific maximum load, e.g. calculated from a specific wind speed at which the wind turbine is stopped. The tower, nacelle, blades and other structures of the wind turbine are designed for this maximum load which means that the structures are sufficiently strong with regard to this maximum wind speed—calculated with a safety margin.
This typically requires increased reinforcement of the heavy turbine parts such as the tower, and the result is increased costs related to manufacturing, handing, maintenance, inspection etc.